The growth and diversity of lightwave networks is placing new demands on optical technology. In particularly, wavelength-division multiplexed (WDM) networks require new optical functions to enable capacity management and provisioning, maintenance, and reliable and robust operation. Obvious functions for WDM optical circuits include multiplexing and demultiplexing at terminal sites and noise filtering in amplified lightwave systems.
Recent WDM network proposals include Add/Drop optical circuits that enable extracting selected channels in a WDM stream and adding replacement channels positioned at the same wavelengths as the dropped channels. (For example, see the "Special Issue on Optical Communication Trends, proceedings of the IEEE, Volume 81, No. 11, November 1993.) The use of Add/Drop optical circuits avoids the electronic demultiplexing required to extract and inject local traffic channels of time-division-multiplexed optical signals. This also allows capacity growth by the creation of additional add/drop channels in the Add/Drop circuit. Add/Drop circuits can be implemented in various ways, including the use of integrated-optic wavelength routers and fiber Bragg grating filters.
Due to the required sharp amplitude transfer function, these filters also have high dispersion. It may be impossible to cascade such filters since the dispersion builds up linearly thereby decreasing the useful bandwidth of the filters. Therefore, it is a problem to manage dispersion in WDM networks employing wavelength selective devices.